The variable %columns is only available in User::new(). Also, it's misspelled in User::get_user(), but even spelling it correctly won't work ;-).

An approach would be to not bless the returned array reference, but bless a hash reference which holds both the array reference with the records, and the column names:

...
my $self = {};
$self->{records} = $sth->fetchall_arrayref();
$self->{columns} = \%columns;
...
[download]

Now, in User::get_user(), you get:

...
return $self->{records}->[$row][{$self}->{columns}->{$field}];
...
[download]

Note, the code is untested, so there could be a syntax error lurking in there somewhere, but I hope I got the point across.

Arjen